A Viking Age barracks

Trelleborg near Slagelse is a Viking ring fortress. It dates back to 980 and was probably built by King Harald Bluetooth or his son Sweyn Forkbeard. It is one of four known ring fortresses that are unique to Danish territory. They are all built according to a strict…

Trelleborg near Slagelse is a Viking ring fortress. It dates back to 980 and was probably built by King Harald Bluetooth or his son Sweyn Forkbeard. It is one of four known ring fortresses that are unique to Danish territory. They are all built according to a strict geometric ground plan with a circular rampart enclosing a number of large houses. In Trelleborg's case, 16 houses nestle within the ramparts. Excavations have uncovered the bodies of more than 150 Vikings buried outside Trelleborg's rampart – including three actual mass graves.

Harald Bluetooth was a king who sought to strengthen the power of the Crown within Danish borders, and to avoid conflicts beyond them. But he was also a skilled diplomat, who understood the importance of making alliances outside of Denmark, such as with the West Slavic communities of Poland.
When he decided to convert the Danes to Christianity and unify Denmark as one realm, he built a number of strategically located fortresses, known as Trelleborgene. The name derives from Trelleborg, a royal fortress west of Slagelse built in circa 980.
Harald Bluetooth had forged strategic alliances through his marriage to Tove, daughter of the Slavic Obotrite Prince Mistivoj. Harald Bluetooth’s son, Sweyn Forkbeard, had married Gunhild, daughter of Mieszco of Poland. Harald Bluetooth died in the Polish town of Wolin, where he had fled after Sweyn had usurped him in the late 980s. Modern archaeology confirms that Denmark in the time of Harald Bluetooth was a multi-ethnic society, as indicated by finds of ceramics and jewellery from the Slavic countries and soapstone vessels and whetstones from Norway. Strontium analysis of skeletal material from the burial site at Trelleborg has confirmed the close contact between Denmark and these regions in the Viking Age.